Class LUFact

A basic decorator class for various methods of LU matrix decomposition.
Note: That if you wish to perform Z = X^(-1)*B you can do this by
LUFact LU = new LUFact(X);
DblMatrix Z = LU.solveSystem(B);
Similarly, if you need to compute L'*B*L where L=X^(-1) you can do
two steps of LU backsubstitution with transposition as in:
LUFact LU = new LUFact(X.transpose());
DblMatrix Z = LU.solveSystem(B);
Z = LU.solveSystem(Z.transpose());
Z = Z.transpose();